Study On Drying Of Wine Grape Pomace

As the major by-products of wine producing, wine grape pomace contain abundantmicroorganisms and moisture, they should be dried immediately to prolong the shelf time, orlots of nutrients would be lost. In this research,“Meili” wine grape pomace were dried withdifferent drying methods,the objectives were to study the drying characteristics and find apropermethod which could be well utilized on the dehydration of the pomace. In this paper,solar drying (SD), convective drying (CD), infrared drying (sequential and consequentialinfrared drying, IR and CIR), and two-stage drying (IR-CD) were used to dry the grapepomace, their drying characteristics (drying rates and drying mathematical models) anddrying quality (quality of dried pomace and the sterilization effects) were analysed, thestructure of grape seeds after dehydration was also observed with Scanning ElectronMicroscope. After the study mentiond above, the best drying method was found, the qualitiesof the products (grape skin and seed ultramicro-pulverised powder) made by the wine grapepomace which were dried by this method were determined and so did the quality variation ofthe wine grape pomace during storage without drying. The main results of the research:1. Compared to CD and IR-CD65°C, IR possessed a much higher drying rate whichreduced at least47.3%of drying time; Midilli and Kucuk model fitted the best; IR andCD-90°Chad the best sterilizing effects and the effects enhaced with drying temperatureincreased, the sterilization effects of IR-CD65°C was better than that of CD but worse than IR;IR had the minimum damage to polyphenols and procyanidins, while CD caused great loss ofthese two ingredients and higher temperatures lead to greater damage, it should be under60°Cto avoid loss of polyphenols and procyanidins.2. Compared to SD, consequential infrared drying (CIR) and two-stage drying (IR-CD),IR also had the highest drying rate; Midilli and Kucuk model fitted the best as well; all thedrying methods owned good sterilizing effects except for SD and IR9min-CD55°C; thecontent of polyphenols and procyanidins experienced different degrees of loss after drying, IRhad a small damaged to polyphenols and also had a better preservation of procyanidins.3. Through the Scanning Electron Microscope (SEM) study, many small holes werefound on the grape seeds’ surface dried by IR, less or no holes were found on that dried by SD or CD. These holes are the main pathways of water transportation, it would be much moredifficult for the moisture to transfer from the inside to the outside without these holes, this iswhy IR had a comparatively higher drying rates.4. Without drying, it was found that with the storage time prolonged, the content of yeastincreased at first and decreased in the next, the content of microorganism and fungaltoxinincreased and the content of phenolic acid decreased; the ultramicro-pulverised powder whichwere stored for1d and dried by IR possessed less microorganism which meant that IR owneda good sterilizing effect; the phenolic acid met with some loss and no influence was found forfungaltoxin.In conclustion, comapred to other drying methods, IR had the highest drying rate, bettersterilization effects and less damage to the functional nurients, it was proved to possess betterdrying quality to wine grape pomace; without drying, some functional nutrients of wine grapepomace lost and the content of microorganism and fungaltoxin increased during storage,therefore, the wine grape pomace shoud be dried immediately avoiding the decrease of theirvalue; many small holes were found on the grape seeds’ surface dried by IR, these holes arethe reason why IR possessed higher drying rates that the other drying methods.